Tolkien's monster concealed flower (6)
I believe the answer is:
orchid
'flower' is the definition.
(orchid is a kind of flower)
'tolkien's monster concealed' is the wordplay.
'tolkien's monster' becomes 'orc' (monster in JRR Tolkien's The Lord of the Rings).
'concealed' becomes 'hid' ('hide' can be a synonym of 'conceal').
'orc'+'hid'='ORCHID'
(Other definitions for orchid that I've seen before include "Flowering plant with bee and lady varieties" , "Lush and expensive tropical flower" , "Ornate flower" , "Often prized flowering plant" , "Plant with complex blooms" .)